In legged mobile robots, in particular, in biped mobile robots of humanoid type, a sensor is installed at each foot to detect displacement of the foot at foot landing or floor reaction force acting on the robot from a floor surface which the robot contacts and based on the detected values, control is appropriately performed to achieve stable walking.
Japanese Laid-Open Patent Application No. Hei 5(1993)-305584 proposes a technique to install the floor reaction force sensor at each robot foot. In the prior art, a six-axis force sensor is installed between an ankle joint and a floor contact end of each foot to detect the floor reaction force acting on the foot.
Further, Journal of the Robotics Society of Japan Vol. 13, No.7, pp. 1030-1037 (October, 1995) proposes a technique to install a displacement sensor detecting the displacement of the feet. In the prior art, a foot of a similar legged mobile robot is made of an upper foot plate and a lower foot plate connected by wire to sandwich a shock absorber therebetween. Sensing elements each comprising a potentiometer (displacement sensors) are disposed at four corners of the upper foot plate, and a converter is installed at its upstream such that distance (displacement) between the upper and lower foot plates is detected through the sensing elements. In this manner, it is detected whether the foot has landed and there is a height difference (irregularity) at a landed floor area.
In the feet of the legged mobile robots, in particular, of the biped mobile robots of humanoid type, it is necessary to install an appropriate guide member to prevent the supporting leg from spinning about the vertical axis due to reaction force of swinging the free leg during robot walking. At the same time, the feet must have certain elasticity to absorb and mitigate the impact at foot landing of the free leg.
When the sensor is thus installed at each foot of the legged mobile robot, in particular, of the biped mobile robots of humanoid type, since space at the feet is limited, the displacement sensor should preferably be compact enough to be installed there. Moreover, in order to achieve a stable walking of the legged mobile robot, it is preferable to detect not only an occurrence of the foot landing but also the floor reaction force acting on the foot.